Hong Kong will quarantine all people arriving from abroad for 14 days, its leader Carrie Lam has said.
The restrictions, which will kick in on Thursday, will not apply to those from Macau or Taiwan. Entrants from mainland China already had to self-isolate.
Ms Lam said the majority of Hong Kong's cases had been imported, adding that "strict measures" were needed.
Hong Kong has seen 57 new infections over the past two weeks, 50 of which were imported, said Ms Lam.
"If we exclude these imported, we only have seven local cases in the past week," she said.
"If we do not impose strict measures, our previous efforts could be wasted."
Ms Lam also advised residents to avoid all non-essential travel.
There are at least 155 confirmed cases in the territory, which detected its first cases in January.
The territory - a special administrative region of China - has so far been able to avoid the contagion seen elsewhere, thanks partly to a quick government response.
In January, cross-border travel with mainland China was slashed. Soon afterwards, health workers went on strike to demand a total border shutdown.
Some of the restrictions in the Asia-Pacific region, as of 17 March:
- Australia - All travellers will have to self-isolate for 14 days. Foreign nationals who have been to China, Iran, Korea and Italy not allowed in
- New Zealand - Everyone entering the country will have to self-isolate for 14 days. This excludes those from small Pacific islands with no confirmed virus cases
- South Korea - Travellers from China's Hubei province not allowed in. International arrivals from certain countries will need to submit papers on their health condition
- Singapore - All visitors with travel history to France, Germany, Italy, Spain, South Korea and China banned from entering or transiting. Residents with recent history to these countries will have to self-isolate for 14 days. All those entering from Japan, Switzerland, the UK and Asean countries will have to self-isolate for 14 days
- Malaysia - All foreign visitors have been banned, all Malaysians will not be allowed to travel overseas until 31 March. All returning Malaysians will have to self quarantine for 14 days
- Japan - Ban on entry to travellers who have been to parts of China, South Korea, Iran or Italy in 14 days before arrival
The number of confirmed coronavirus cases and deaths outside China has now surpassed the number inside.
More than 100,000 people have been infected outside China, while just over 80,000 cases have been reported inside.
There have been more than 182,000 confirmed cases of coronavirus globally and over 7,000 deaths, according to a tally from Johns Hopkins University.